Samsung was quick to adopt wireless charging in its Galaxy phones, but the technology’s popularity has reached an all time high thanks to its adoption in Apple’s iPhones last year. A potentially tricky standards war also seems to have been won by the Wireless Power Consortium with the wide adoption of the Qi standard.
We’ve been big fans of wireless charging for a few years now. Not having to fumble around with a cable when you want to charge up your phone’s battery is great, especially if it’s dark and you’re trying to avoid waking your partner. But as wireless charging has taken off, a few people have started to ask if there’s a hidden cost. We’ve seen a few articles, forum discussions, and comments suggesting that wireless charging might degrade your battery faster than traditional wired charging. We decided to investigate and find out if there’s any truth to this supposition.
HOW DOES A PHONE BATTERY WORK?
Our smartphones use lithium-ion batteries. Cells have two electrodes – a cathode and an anode — with an electrolyte in between which allows the lithium ions to move between the electrodes. When you charge they go from positive to negative, and when you discharge they move in the opposite direction.
“Electrical energy is changed into chemical energy during charging and the reverse happens during discharge,” Dr. Daniel Abraham, senior scientist at the Argonne Laboratory, told Digital Trends.
The battery manufacturer decides how much energy can be stored in the cell, and that determines how much energy you have available to use.
“The manufacturer decides the upper cut off voltage and the lower cut off voltage, which are fixed, and cells cycle between the two voltage ranges,” Dr. Abraham explained. “As long as you choose the voltage range appropriately, you can cycle the cell thousands of times.”
“It doesn’t matter if you have a wireless or wired charger.”
It’s not possible to exceed these limits by leaving your phone on the wireless charging pad for too long, or by leaving it plugged in overnight. You also can’t drain the cell beyond the lower cut off limit dictated by the manufacturer. These limits don’t distinguish between power sources.
“It doesn’t matter if you have a wireless or wired charger,” Dr. Abraham said. “You won’t be able to overcharge or over-discharge a cell.”
WHAT ABOUT CYCLE LIMITS?
Different batteries have different standards, but it’s accepted that beyond a certain number of charge cycles, a battery is going to degrade. In the case of Apple’s iPhone devices, for example, batteries are designed to retain up to 80 percent of original capacity after 500 complete charge cycles.
One of the criticisms levelled at wireless charging, as explained in this ZDNet article, is that when phones charge via the cable the battery gets a rest, but when they charge on a wireless charging pad it doesn’t. Therefore, the battery goes through its limited number of cycles faster with wireless charging and degrades faster. But is this true?
“A phone’s battery is not drained when you use it while charging wirelessly,” Menno Treffers, chairman of the Wireless Power Consortium, told Digital Trends. “This is a misunderstanding.”
“A phone’s battery is not drained when you use it while charging wirelessly.”
If you want to slow down charge cycles, the simplest way is to cut the amount of power you use. A rogue app that’s continually sending data in the background, or an area of poor cell connectivity where your phone is trying to boost the signal to connect, are both potentially more damaging to your battery longevity than your charging habits.
As you would expect, the manufacturing process is also important in determining battery longevity.
“The quality of the materials used makes a big difference to how long the battery lasts,” Dr. Abraham explained. “You may end up getting what you pay for.”
POTENTIAL BENEFITS OF WIRELESS CHARGING
While there doesn’t seem to be any evidence that wireless charging degrades your smartphone battery faster than wired charging, there are a few tangible benefits. Wear and tear on the charging port is reduced, something that often leads to faults and requires repair.
“The chargers themselves also have no wear and tear,” Treffers said. “That is ideal for public charging infrastructure in hotels, vehicles, restaurants, and trains.”
Then there’s the idea that you should ideally keep your battery partially charged. We looked into whether it’s okay to leave your smartphone plugged into the charger overnight before, and got the advice that your battery will last longer if it stays between 50 and 80 percent.
“By continually topping up the phone battery during the day, as you might do with wireless charging, and not letting your phone battery dip below 50%, you will actually increase the lifespan of your battery,” Treffers claimed. “According to research we have seen, battery lifetime actually increases by 4x when the depth of discharge – or amount that the battery is drained – is limited to 50 percent, rather than 100 percent.”
So far, so good, but wireless charging isn’t perfect. Apart from the slower charging speed, it’s also important to consider temperature.
FEELING THE HEAT
“Performance degradation of cells is affected by time, temperature, and voltage limit,” Dr. Abraham explained. “To increase the amount of energy stored in the cell, manufacturers keep pushing the voltage limits.”
We can’t stop time, and the voltage limits are set by the manufacturer, so that leaves temperature.
“Performance degradation of cells is affected by time, temperature, and voltage limit.”
Have you ever noticed your phone heating up when it’s wirelessly charging? If you charge it up with a case on, or you don’t have it properly seated on the charging pad, then you might notice that it gets even warmer.
“Most phone batteries are damaged by exposure to heat, which is why it’s important to ensure that the charger is Qi-certified,” Treffers explained. “Certified devices are tested rigorously to help ensure safety, interoperability and energy efficiency – this helps to ensure that temperatures do not rise to dangerous or damaging levels.”
It seems that temperature, rather than charging routine, is what we should be paying attention to if we want our smartphone batteries to last for as long as possible. Many of the best wireless chargers have fans and cooling systems built in. But it’s not an issue that’s confined to wireless charging – you probably notice your phone heating up when it’s plugged in too.
If you’re concerned, then don’t leave your phone sitting in direct sunlight on the windowsill or in a hot car. Don’t use your phone to play a graphically-intensive game while it’s plugged in and charging. And don’t use uncertified wireless charging pads or wired chargers.
Ultimately, much depends on the manufacture process, the settings that phone makers select, and how you use your phone, but as charging speeds and battery capacity are pushed ever higher, battery longevity may be a casualty.
We’ve noticed that fast charging via wired chargers, technology that is getting speedier all the time, can make your phone very hot, which can’t be good for the battery, but that’s another question. As for this one – the short answer is no, wireless charging does not degrade your battery faster.